LEDs are light sources that are being developed to replace conventional lighting systems, such as fluorescent and incandescent lights, in order to provide more energy efficient systems. Since an incandescent light source typically consumes 60-100 W and has a short lifetime, an LED bulb would be the excellent substitute with considerably less power dissipation and longer life. There has therefore been much research into the development of an LED bulb compatible with TRIAC dimmers, which are common in lighting systems.
A major issue with TRIAC dimmable LED bulbs is dimmer compatibility. The conventional TRIAC dimmer was designed to handle hundreds of watts induced by incandescent bulbs. An LED bulb consuming much less power will interact with those dimmers composed of high-power devices. If the interaction between dimmer and LED bulb is not stabilized, visible flicker is perceptible.
In order to prevent visible flicker, a conventional TRIAC dimmer needs a latching current at firing and a holding current during the TRIAC turn-on after firing. If those two currents are not met, the TRIAC dimmer misfires and the LED light source flickers.
The latching and holding currents are different between different dimmer models. The typical range of latching and holding currents is around 5˜50 mA. Those operating requirements do not cause problems when incandescent bulbs are used, due to their high power consumption. However, an LED bulb with much less output power cannot maintain this amount of current over the whole line cycle without additional circuitry.
Conventional power adaptors typically require a second stage that provides compatibility, but this increases costs. It is also known to regulate the LEDs themselves in an attempt to reduce or eliminate flicker, even though the power supply is unstable.
There have now been devised improved power adaptors which overcome or substantially mitigate the above-mentioned and/or other disadvantages associated with the prior art.